Acoustic wave device with multi-layer interdigital transducer electrode

ABSTRACT

An acoustic wave device includes a piezoelectric layer and an interdigital transducer electrode disposed over the piezoelectric layer. The interdigital transducer electrode is thicker in a center region of the interdigital transducer electrode than in a gap region of the interdigital transducer electrode to thereby reduce a mass loading of the interdigital transducer electrode in the gap region. The interdigital transducer electrode has a layer of less dense material disposed of a layer of more dense material.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

Any and all applications for which a foreign or domestic priority claimis identified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND Technical Field

Embodiments of this disclosure relate to acoustic wave devices, and moreparticularly to acoustic wave devices with a multi-layer interdigitaltransducer electrode.

Description of Related Technology

Acoustic wave filters can be implemented in radio frequency electronicsystems. For instance, filters in a radio frequency front end of amobile phone can include acoustic wave filters. An acoustic wave filtercan filter a radio frequency signal. An acoustic wave filter can be aband pass filter. A plurality of acoustic wave filters can be arrangedas a multiplexer. For example, two acoustic wave filters can be arrangedas a duplexer.

An acoustic wave filter can include a plurality of resonators arrangedto filter a radio frequency signal. Example acoustic wave filtersinclude surface acoustic wave (SAW) filters and bulk acoustic wave (BAW)filters. A surface acoustic wave resonator can include an interdigitaltransductor electrode on a piezoelectric substrate. The surface acousticwave resonator can generate a surface acoustic wave on a surface of thepiezoelectric layer on which the interdigital transductor electrode isdisposed.

SUMMARY OF CERTAIN INVENTIVE ASPECTS

The innovations described in the claims each have several aspects, nosingle one of which is solely responsible for its desirable attributes.Without limiting the scope of the claims, some prominent features ofthis disclosure will now be briefly described.

In accordance with one aspect of the disclosure, an acoustic wave deviceis provided. The acoustic wave device comprises a piezoelectric layer.An interdigital transducer electrode is disposed over the piezoelectriclayer, the interdigital transducer electrode being thicker in a centerregion of the interdigital transducer electrode than in a gap region ofthe interdigital transducer electrode to thereby reduce a mass loadingof the interdigital transducer electrode in the gap region.

In accordance with another aspect of the disclosure, an acoustic wavedevice is provided. The acoustic wave device comprises a piezoelectriclayer. An interdigital transducer electrode includes a first layerdisposed over the piezoelectric layer and a second layer disposed overthe first layer, the second layer being of a less dense material thanthe first layer. A thickness of the first layer in a gap region of theinterdigital transducer electrode is smaller than a thickness of thefirst layer in a center region of the interdigital transducer electrodeto thereby reduce a mass loading of the interdigital transducerelectrode in the gap region.

In accordance with another aspect of the disclosure, an acoustic wavefilter is provided. The acoustic wave filter comprises an acoustic wavedevice including a piezoelectric layer and a multi-layer interdigitaltransducer electrode including a first layer disposed over thepiezoelectric layer and a second layer disposed over the first layer,the second layer being of a less dense material than the first layer. Athickness of the first layer in a gap region of the interdigitaltransducer electrode is smaller than a thickness of the first layer in acenter region of the interdigital transducer electrode to thereby reducea mass loading of the interdigital transducer electrode in the gapregion. The acoustic wave filter also comprises a plurality ofadditional acoustic wave devices, the acoustic wave device and theplurality of additional acoustic wave devices together configured tofilter a radio frequency signal.

In accordance with another aspect of the disclosure, a radio frequencymodule is provide. The radio frequency module comprises a packagesubstrate and an acoustic wave filter configured to filter aradiofrequency signal. The acoustic wave filtering includes an acousticwave resonator that includes a piezoelectric layer and an interdigitaltransducer electrode including a first layer disposed over thepiezoelectric layer and a second layer disposed over the first layer,the second layer being of a less dense material than the first layer Athickness of the first layer in a gap region of the interdigitaltransducer electrode is smaller than a thickness of the first layer in acenter region of the interdigital transducer electrode to thereby reducea mass loading of the interdigital transducer electrode in the gapregion. The radiofrequency module also comprises additional circuitry,the acoustic wave filter and additional circuitry disposed on thepackage substrate.

In accordance with another aspect of the disclosure a wirelesscommunication device is provided. The wireless communication devicecomprises an antenna and a front end module including an acoustic wavefilter configured to filter a radio frequency signal associated with theantenna. The acoustic wave filter includes one or more acoustic wavedevices that each include a piezoelectric layer and an interdigitaltransducer electrode including a first layer disposed over thepiezoelectric layer and a second layer disposed over the first layer,the second layer being of a less dense material than the first layer. Athickness of the first layer in a gap region of the interdigitaltransducer electrode is smaller than a thickness of the first layer in acenter region of the interdigital transducer electrode to thereby reducea mass loading of the interdigital transducer electrode in the gapregion.

In accordance with another aspect of the disclosure, a method ofmanufacturing an acoustic wave device is provided. The method comprisesforming or providing a piezoelectric layer and forming or providing aninterdigital transducer electrode over the piezoelectric layer. Theinterdigital transducer electrode includes a first layer over thepiezoelectric layer and a second layer over the first layer, the secondlayer being of a less dense material than the first layer. A thicknessof the first layer in a gap region of the interdigital transducerelectrode is smaller than a thickness of the first layer in a centerregion of the interdigital transducer electrode to thereby reduce a massloading of the interdigital transducer electrode in the gap region.

In accordance with another aspect of the disclosure, an acoustic wavedevice is provided. The acoustic wave device comprises a piezoelectriclayer and an interdigital transducer electrode. The interdigitaltransducer electrode includes a first layer disposed over thepiezoelectric layer and a second layer disposed over the first layer,the second layer being of a more dense material than the first layer. Athickness of the second layer in a gap region of the interdigitaltransducer electrode is smaller than a thickness of the second layer ina center region of the interdigital transducer electrode to therebyreduce a mass loading of the interdigital transducer electrode in thegap region.

In accordance with another aspect of the disclosure, an acoustic wavefilter is provided. The acoustic wave filter comprises an acoustic wavedevice including a piezoelectric layer and a multi-layer interdigitaltransducer electrode including a first layer disposed over thepiezoelectric layer and a second layer disposed over the first layer,the second layer being of a more dense material than the first layer. Athickness of the second layer in a gap region of the interdigitaltransducer electrode is smaller than a thickness of the second layer ina center region of the interdigital transducer electrode to therebyreduce a mass loading of the interdigital transducer electrode in thegap region. The acoustic wave filter also comprises a plurality ofadditional acoustic wave devices, the acoustic wave device and theplurality of additional acoustic wave devices together configured tofilter a radio frequency signal.

In accordance with another aspect of the disclosure a radio frequencymodule is provided. The radio frequency module comprises a packagesubstrate and an acoustic wave filter configured to filter aradiofrequency signal. The acoustic wave filter includes an acousticwave resonator that includes a piezoelectric layer and an interdigitaltransducer electrode including a first layer disposed over thepiezoelectric layer and a second layer disposed over the first layer,the second metal layer being of a more dense material than the firstlayer. A thickness of the second layer in a gap region of theinterdigital transducer electrode is smaller than a thickness of thesecond layer in a center region of the interdigital transducer electrodeto thereby reduce a mass loading of the interdigital transducerelectrode in the gap region. The radio frequency module also comprisesadditional circuitry, the acoustic wave filter and additional circuitrydisposed on the package substrate.

In Accordance with another aspect of the disclosure, a wirelesscommunication device is provided. The wireless communication devicecomprises an antenna and a front end module including an acoustic wavefilter configured to filter a radio frequency signal associated with theantenna. The acoustic wave filter includes one or more acoustic wavedevices that each include a piezoelectric layer and an interdigitaltransducer electrode including a first layer disposed over thepiezoelectric layer and a second layer disposed over the first layer,the second layer being of a more dense material than the first layer. Athickness of the second layer in a gap region of the interdigitaltransducer electrode is smaller than a thickness of the second layer ina center region of the interdigital transducer electrode to therebyreduce a mass loading of the interdigital transducer electrode in thegap region.

In accordance with another aspect of the disclosure, a method ofmanufacturing an acoustic wave device is provided. The method comprisesforming or providing a piezoelectric layer. The method also comprisesforming or providing an interdigital transducer electrode over thepiezoelectric layer, the interdigital transducer electrode including afirst layer over the piezoelectric layer and a second layer over thefirst layer, the second layer being of a more dense material than thefirst layer. A thickness of the second layer in a gap region of theinterdigital transducer electrode is smaller than a thickness of thesecond layer in a center region of the interdigital transducer electrodeto thereby reduce a mass loading of the interdigital transducerelectrode in the gap region.

In accordance with another aspect of the disclosure, an acoustic wavefilter is provided. The acoustic wave filter comprises a piezoelectriclayer. The acoustic wave filter also comprises a first acoustic wavedevice including a first portion of the piezoelectric layer and a firstmulti-layer interdigital transducer electrode disposed over the firstportion of the piezoelectric layer. The acoustic wave filter alsocomprises a plurality of additional acoustic wave devices coupled to thefirst acoustic wave device, the plurality of additional acoustic wavedevices including a second portion of the piezoelectric layer and aplurality of multi-layer interdigital transducer electrodes disposedover the second portion of the piezoelectric layer. At least one of theplurality of multi-layer interdigital transducer electrodes includes ametal layer that is thinner than a corresponding metal layer of the samematerial of the first multi-layer interdigital transducer electrode ofthe first acoustic wave device.

In accordance with another aspect of the disclosure, an acoustic wavefilter is provided. The acoustic wave filter comprises an acoustic wavedevice including a first portion of a piezoelectric layer and amulti-layer interdigital transducer electrode disposed over the firstportion of the piezoelectric layer. The acoustic wave filter alsocomprises a multi-mode surface acoustic wave filter coupled to theacoustic wave device, the multi-mode surface acoustic wave filterincluding a second portion of the piezoelectric layer and a plurality ofmulti-layer interdigital transducer electrodes disposed over the secondportion of the piezoelectric layer and longitudinally coupled to eachother. At least one of the plurality of multi-layer interdigitaltransducer electrodes includes a metal layer that is thinner than acorresponding metal layer of the same material of the multi-layerinterdigital transducer electrode of the acoustic wave device.

In accordance with another aspect of the disclosure, a radio frequencymodule is provided. The radio frequency module comprises a packagesubstrate and an acoustic wave filter configured to filter aradiofrequency signal. The acoustic wave filter includes a firstacoustic wave device including a first portion of a piezoelectric layerand a first multi-layer interdigital transducer electrode disposed overthe first portion of the piezoelectric layer. The acoustic wave filteralso comprises a plurality of additional acoustic wave devices coupledto the first acoustic wave device. The plurality of additional acousticwave devices include a second portion of the piezoelectric layer and aplurality of multi-layer interdigital transducer electrodes disposedover the second portion of the piezoelectric layer. At least one of theplurality of multi-layer interdigital transducer electrodes includes ametal layer that is thinner than a corresponding metal layer of the samematerial of the first multi-layer interdigital transducer electrode ofthe first acoustic wave device. The radio frequency module alsocomprises additional circuitry, the acoustic wave filter and additionalcircuitry disposed on the package substrate.

In accordance with another aspect of the disclosure, a wirelesscommunication device is provided. The wireless communication devicecomprises an antenna and a front end module including an acoustic wavefilter configured to filter a radio frequency signal associated with theantenna. The acoustic wave filter includes a first acoustic wave deviceincluding a first portion of a piezoelectric layer and a firstmulti-layer interdigital transducer electrode disposed over the firstportion of the piezoelectric layer. The acoustic wave filter alsoincludes a plurality of additional acoustic wave devices coupled to thefirst acoustic wave device. The plurality of additional acoustic wavedevices include a second portion of the piezoelectric layer and aplurality of multi-layer interdigital transducer electrodes disposedover the second portion of the piezoelectric layer. At least one of theplurality of multi-layer interdigital transducer electrodes includes ametal layer that is thinner than a corresponding metal layer of the samematerial of the first multi-layer interdigital transducer electrode ofthe first acoustic wave device.

In accordance with another aspect of the disclosure, a method ofmanufacturing an acoustic wave filter is provided. The method comprisesforming or providing a piezoelectric layer. The method also comprisesforming or providing a first multi-layer interdigital transducerelectrode over the first portion of the piezoelectric layer. The methodalso comprises forming or providing a plurality of multi-layerinterdigital transducer electrodes over the second portion of thepiezoelectric layer. At least one of the plurality of multi-layerinterdigital transducer electrodes includes a metal layer that isthinner than a corresponding metal layer of the same material of thefirst multi-layer interdigital transducer electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of this disclosure will now be described, by way ofnon-limiting example, with reference to the accompanying drawings.

FIG. 1A illustrates a cross-section of a surface acoustic wave (SAW)device including a multi-layer interdigital transducer electrode.

FIG. 1B is a top plan view of the surface acoustic wave device of FIG.1A.

FIG. 1C illustrates a cross-section of a surface acoustic wave (SAW)device including a multi-layer piezoelectric substrate.

FIG. 1D illustrates a cross-sectional view of a surface acoustic wave(SAW) device including an interdigital transducer electrode.

FIG. 1E is a top plan view of the surface acoustic wave device of FIG.1D.

FIG. 2 is a top plan view of a resonator incorporating the surfaceacoustic wave device of FIGS. 1A-1B.

FIG. 3 is a top plan view of a multi-mode surface acoustic wave filterincorporating the surface acoustic wave device of FIGS. 1A-1B.

FIG. 4A is an illustration of one step in a process of making theresonator of FIG. 2.

FIG. 4B is an illustration of another step in a process of making theresonator of FIG. 2.

FIG. 4C is an illustration of another step in a process of making theresonator of FIG. 2.

FIG. 5A illustrates a cross-section of a surface acoustic wave (SAW)device including a multi-layer interdigital transducer electrode.

FIG. 5B is a top plan view of the surface acoustic wave device of FIG.5A.

FIG. 5C illustrates a cross-section of a surface acoustic wave (SAW)device including a multi-layer piezoelectric substrate.

FIG. 5D illustrates a cross-section of a surface acoustic wave (SAW)device including a multi-layer interdigital transducer electrode.

FIG. 5E is a top plan view of the surface acoustic wave device of FIG.5D.

FIG. 5F illustrates a cross-section of a surface acoustic wave (SAW)device including a multi-layer interdigital transducer electrode.

FIG. 5G illustrates a cross-section of a surface acoustic wave (SAW)device including a multi-layer interdigital transducer electrode.

FIG. 5H is a top plan view of the surface acoustic wave device of FIG.5G.

FIG. 6A is an illustration of one step in a process of making aresonator including the SAW device of FIG. 5A.

FIG. 6B is an illustration of another step in a process of making aresonator including the SAW device of FIG. 5A.

FIG. 6C is an illustration of another step in a process of making aresonator including the SAW device of FIG. 5A.

FIG. 7 is a top plan view of a surface acoustic wave filter.

FIG. 8A is a top plan view of multiple surface acoustic wave devicesdisposed on a single substrate.

FIG. 8B illustrates a cross-section of the surface acoustic wave devicesof FIG. 8A.

FIG. 9A is a top plan view of multiple surface acoustic wave devicesdisposed on a single substrate.

FIG. 9B illustrates a cross-section of the surface acoustic wave devicesof FIG. 9A.

FIG. 10A is a top plan view of multiple surface acoustic wave devicesdisposed on a single substrate.

FIG. 10B illustrates a cross-section of the surface acoustic wavedevices of FIG. 10A.

FIGS. 11A to 11E are diagrams of IDTs of piston mode Lamb waveresonators according to various embodiments. FIG. 11A illustrates an IDTwith fingers having hammer head shaped end portions. FIG. 11Billustrates an IDT with thicker portions for both border regions of eachfinger. FIG. 11C illustrates an IDT with fingers having hammer headshaped end portions and bus bars having extension portions adjacent tothe end portions of the fingers. FIG. 11D illustrates an IDT withthicker end portions on border regions of each finger and bus barshaving extension portions adjacent to end portions of the fingers. FIG.11E illustrates an IDT with fingers having thicker end portions andthicker regions extending from a bus bar toward an active region. FIG.11F illustrates an IDT with a second narrow busbar and FIG. 11Gillustrates a cross-section of a surface acoustic wave (SAW) deviceincluding the IDT of FIG. 11F. FIG. 11H illustrates an IDT with adisconnected second narrow busbar and FIG. 11I illustrates across-section of a surface acoustic wave (SAW) device including the IDTof FIG. 11H. FIG. 11J illustrates an IDT with a floating mass loadingstrip and FIG. 11K illustrates a cross-section of a surface acousticwave (SAW) device including the IDT of FIG. 11J.

FIG. 12 is a schematic diagram of a radio frequency module that includesa surface acoustic wave component according to an embodiment.

FIG. 13 is a schematic diagram of a radio frequency module that includesduplexers with surface acoustic wave resonators according to anembodiment.

FIG. 14 is a schematic block diagram of a module that includes a poweramplifier, a radio frequency switch, and duplexers that include one ormore surface acoustic wave resonators according to an embodiment.

FIG. 15 is a schematic block diagram of a module that includes anantenna switch and duplexers that include one or more surface acousticwave resonators according to an embodiment.

FIG. 16 is a schematic block diagram of a wireless communication devicethat includes a filter in accordance with one or more embodiments.

FIG. 17 is a schematic block diagram of another wireless communicationdevice that includes a filter in accordance with one or moreembodiments.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

The following description of certain embodiments presents variousdescriptions of specific embodiments. However, the innovations describedherein can be embodied in a multitude of different ways, for example, asdefined and covered by the claims. In this description, reference ismade to the drawings where like reference numerals can indicateidentical or functionally similar elements. It will be understood thatelements illustrated in the figures are not necessarily drawn to scale.Moreover, it will be understood that certain embodiments can includemore elements than illustrated in a drawing and/or a subset of theelements illustrated in a drawing. Further, some embodiments canincorporate any suitable combination of features from two or moredrawings.

Acoustic wave filters can filter radio frequency (RF) signals in avariety of applications, such as in an RF front end of a mobile phone.An acoustic wave filter can be implemented with surface acoustic wave(SAW) resonators. The speed at which an acoustic wave will propagatewithin a SAW resonator is a function of a variety of factors, includingthe thicknesses of the various components and the density of thematerials used to form the various components.

A plurality of resonators may be formed on a single wafer, includingfilter components of different types. For example, a single wafer mayinclude one or more multi-mode SAW filters, in addition to one or moreSAW resonators. These components may have different design, but mayshare common manufacturing steps, and may therefore share commonconstituent layers. The use of thicker layers and/or denser materials inan interdigital transducer (IDT) electrode of a SAW resonator can slowthe propagation of acoustic waves within the SAW resonators, allowingthe SAW resonators to be made more compact. However, the use of thesethicker layers or denser materials in IDT electrodes may not be suitablefor use in the longitude coupled multi-mode SAW filters.

Aspects of this disclosure relate to the reduction in side leakage in aSAW device by reducing the mass loading in the gap region, such as byreplacing a heavy or denser material of the IDT with a lighter or lessdense material.

FIG. 1A illustrates a cross-section of a surface acoustic wave (SAW)resonator including a multilayer interdigital transducer electrode. FIG.1B is a top plan view of the surface acoustic wave resonator of FIG. 1A.The illustrated SAW resonator 100 in includes a piezoelectric layer 102.In some embodiments, the piezoelectric layer 102 may include a materialsuch as lithium tantalate (LT) or lithium niobate (LN), although othersuitable materials may also be used.

The SAW resonator 100 also includes an interdigital transducer (IDT)electrode 110. The IDT electrode 110 can include any suitable IDTelectrode material. In the illustrated embodiment, the IDT electrode 110is a multi-layer IDT electrode that includes separate IDT electrodelayers that impact acoustic properties (e.g., IDT sublayer with moredense material, such as tungsten (W)) and electrical properties (e.g.,IDT sublayer with less dense material, such as Aluminum (Al)),respectively. The IDT electrode 110 includes a first IDT sublayer 111and a second IDT sublayer 113. In some embodiments the first IDTsublayer 111 can be of a material with a higher density than thematerial of the second IDT sublayer 113. In some embodiments, the firstIDT sublayer 111 may include tungsten (W) and the second IDT sublayer113 may include Aluminum (Al). Other suitable materials can be used forthe first IDT sublayer 111 and/or second IDT sublayer 113, such asAluminum (Al) copper (Cu), Magnesium (Mg), tungsten (W), titanium (Ti),or other suitable materials, as well as any suitable combinationthereof. In some embodiments, the IDT electrode 110 may include alloys,such as AlMgCu, AlCu, etc. For example, the first IDT sublayer 111 mayinclude molybdenum (Mo).

A temperature compensation layer 130 is located over the IDT electrode110. In some embodiments, the temperature compensation layer 130 mayinclude a layer of silicon dioxide (SiO2) or other silica oxide-basedmaterial, although other suitable materials may also be used. In the SAWresonator 100 the temperature compensation layer 130 can bring atemperature coefficient of frequency (TCF) of the SAW resonator 100closer to zero. The temperature compensation layer 130 can have apositive TCF. This can compensative for a negative TCF of thepiezoelectric layer 102, as various piezoelectric layers such as lithiumniobate and lithium tantalate have a negative TCF. A passivation layer150 is located over the temperature compensation layer 130. Thepassivation layer 150 may include, for example, a layer of siliconnitride (SiN) or a layer of silicon oxynitride (SiON), although othersuitable materials may also be used.

In the illustrated embodiment, strips 142 (e.g., mass loading strips,metal strips, such as high density metal strips of any suitable metalwith a density equal to or greater than a layer of the IDT electrode110) are located over edge regions of the IDT 110 electrode. As can beseen in FIG. 1B, the IDT electrode 110 can include a bus bar 112 andfingers 114 that extend from the bus bar 112 toward the opposite busbar, with a gap portion or region 118 located between the ends of thefingers 114 and the opposite bus bar. The gap portions 118 can have awidth W₂. In some embodiments the gap portions 118 may have a width ofabout 0.9 k, although other suitable widths may also be used. Thefingers 114 of the IDT electrode 110 have an active region. The activeregion can be a region between the gap portions 118. This region can bereferred to as an aperture 126, having a width W₃. The edge portions 124on either side of a central region 128 of the active region or aperture126 have widths W₁. In some embodiments the edge portions 124 may have awidth of about 0.5 to 1.5λ, although other suitable widths may also beused. The strips 142 can overlie edge portions of fingers 114 of the IDTelectrode 110 as illustrated, and can have the same width W₁ as the edgeportions 124.

In the illustrated embodiment, the first IDT sublayer 111 has athickness T₂, the second IDT sublayer 113 has a thickness T₃, and thetemperature compensation layer 130 has a thickness of T₁ within the gapregions 118. In some embodiments, the thickness T₂ may be between about0.02λ and 0.1λ, although other thicknesses may also be used. In someembodiments, the thickness T₃ may be between about 0.02λ and 0.1λ,although other thicknesses may also be used. In some embodiments, thethickness T₁ of the temperature compensation layer 130 may be betweenabout 0.2λ and 0.5λ, although other thicknesses may also be used.

With continued reference to FIG. 1A, the IDT 110 has reduced massloading in the gap portion or region 118. As illustrated in FIG. 1A, inone implementation the first IDT sublayer 111 is removed (e.g.,completely removed) in the gap region 118 and filled by the material ofthe second IDT sublayer 113, where the material of the second IDTsublayer 113 is less dense than the material of the first IDT sublayer111. Therefore, in one implementation, there is only one IDT layer inthe gap region 118 (e.g., the second IDT sublayer 113). In anotherimplementation, some but less than all (e.g., ½) of the material of thefirst IDT sublayer 111 is removed in the gap region 118 so that thefirst IDT sublayer 111 is thinner in the gap region 118 relative toother portions of the first IDT sublayer 111. The thickness of the IDT110 in the gap region 118 is smaller relative to other portions of theIDT 110. As further described below, the IDT 110 can be formed by firstapplying the first IDT sublayer 111, then removing (e.g., etching) someor all of the material of the first IDT sublayer 111 in the gap region118. Then the second IDT sublayer 113 is applied. Advantageously,removing at least some (e.g., ½, removing all) of the first IDT sublayer111 in the gap region 118 so that the second IDT sublayer 113 providesthe majority (e.g., all) of the IDT material in the gap region 118reduces mass loading in the gap region 118 to inhibit (e.g., reduce) Qdegradation from resonant frequency (e.g., as a result of edge shearhorizontal mode radiation).

FIG. 1C illustrates a cross-section of a surface acoustic wave resonatorincluding a multi-layer piezoelectric substrate. The SAW resonator 100′of FIG. 1C is similar to the SAW resonator 100 in FIGS. 1A-1B. Thus,reference numerals used to designate the various components of the SAWresonator 100′ are identical to those used for identifying thecorresponding components of the SAW resonator 100 in FIGS. 1A-1B.Therefore, the structure and description above for the various featuresof the SAW resonator 100 in FIGS. 1A-1B are understood to also apply tothe corresponding features of the SAW resonator 100′ in FIG. 1C, exceptas described below.

The SAW resonator 100′ includes a multilayer piezoelectric substrate106, including a support substrate 104 in addition to the piezoelectricsubstrate 102. The support substrate 104 may include silicon (Si) insome embodiments, although other suitable materials may also be used,including but not limited to sapphire, aluminum oxide (Al₂O₃), aluminumnitride (AlN), or ceramic materials. Although the multilayerpiezoelectric substrate 106 is illustrated as including two layers, oneor more additional layers may also be included. For example, in someembodiments, the multilayer piezoelectric substrate may include afunctional layer, such as an SiO₂ layer, between the piezoelectricsubstrate 102 and the support substrate 104. A multi-layer piezoelectricsubstrate can be implemented in accordance with any suitable principlesand advantages disclosed herein.

FIG. 1D illustrates a cross-section of a surface acoustic wave (SAW)resonator 100″ including a multilayer interdigital transducer electrode.FIG. 1E is a top plan view of the surface acoustic wave resonator ofFIG. 1D. The illustrated SAW resonator 100″ is similar to the SAWresonator 100 in FIGS. 1A-1B. Thus, reference numerals used to designatethe various components of the SAW resonator 100″ are identical to thoseused for identifying the corresponding components of the SAW resonator100 in FIGS. 1A-1B. Therefore, the structure and description above forthe various features of the SAW resonator 100 in FIGS. 1A-1B areunderstood to also apply to the corresponding features of the SAWresonator 100″ in FIG. 1D-1E, except as described below.

The SAW resonator 100″ differs from the SAW resonator 100 in that thebus bars 112 of the IDT 110 each include extension portions, such asextension portion 119, in the gap region 118 that are spaced from endportions of fingers 114 of the IDT 110. The extension portions 119 canbe dummy electrodes. As shown in FIG. 1D, the extension portions 119 areformed by the first IDT sublayer 111 (e.g., but not the second IDTsublayer 113).

FIG. 2 illustrates a top plan view of a resonator R incorporating thesurface acoustic wave device 100 (e.g., of FIGS. 1A-1B) between a pairof acoustic reflectors 300. The acoustic reflectors 300 are separatedfrom the IDT electrode 110 of the SAW device 100 by respective gaps. Inother implementations, the resonator R can instead have the SAW device100′ of FIG. 1C or SAW device 100″ of FIGS. 1D-1E between the acousticreflectors 300.

FIG. 3 illustrates a top plan view of a multi-mode surface acoustic wavefilter F incorporating the surface acoustic wave device 100 (e.g., ofFIGS. 1A-1B). in the illustrated implementation, the filter F has threeSAW devices 100 (e.g., arranged sequentially) between a pair of acousticreflectors 300. The SAW device 100 can be spaced from each other by agap. The acoustic reflectors 300 are separated from the IDT electrode110 of its adjacent SAW device 100 by respective gaps. In otherimplementations, the multi-mode SAW filter F can instead have one ormore SAW devices 100′ of FIG. 1C or one or more SAW devices 100″ ofFIGS. 1D-1E between the acoustic reflectors 300. In the illustratedimplementation, the strips 142 (e.g., mass loading strips) extend pastthe edge of the fingers of the IDT. In another implementation, thestrips 142 (e.g., mass loading strips) do not extend past the edge ofthe fingers of the IDT; for example, the end edge of the strips 142 canalign with the edge of the fingers of the IDT. In the illustratedimplementation, the strips 142 (e.g., mass loading strips) extend overthe entirety of the reflectors 300. In other implementations, the strips142 can extend over a portion of (but less than all of) the reflectors300. In another implementation, the strips 142 do not extend over thereflectors 300.

FIGS. 4A-4C show steps in a process for making the IDT of the resonatorR (e.g., in FIG. 2). As shown in FIG. 4A, the first IDT sublayer 111 isapplied (e.g., deposited), for example, over the piezoelectric layer 102and patterned. In one example, the first IDT sublayer 111 can be made oftungsten (W). As shown in FIG. 4B, the second IDT sublayer 113 isapplied (e.g., deposited), for example, on the first IDT sublayer 111and the first and second IDT sublayers 111, 113 are patterned to definethe IDT structure of the SAW device 100 and the acoustic reflectors 300.In one example, the second IDT sublayer 113 can be made of Aluminum(Al). As shown in FIG. 4C, the piston mode layer or strips (e.g., massloading strips) 142 can then be applied over the edge regions of the IDT110 and patterned.

FIG. 5A illustrates a cross-section of a surface acoustic wave (SAW)resonator including a multilayer interdigital transducer electrode. FIG.5B is a top plan view of the surface acoustic wave resonator of FIG. 5A.The illustrated SAW resonator 200 in includes a piezoelectric layer 202.In some embodiments, the piezoelectric layer 202 may include a materialsuch as lithium tantalate (LT) or lithium niobate (LN), although othersuitable materials may also be used.

The SAW resonator 200 also includes an interdigital transducer (IDT)electrode 210. The IDT electrode 210 can include any suitable IDTelectrode material. In the illustrated embodiment, the IDT electrode 210includes a first IDT sublayer 211 and a second IDT sublayer 213. In someembodiments the first IDT sublayer 211 can be of a material with a lowerdensity than the material of the second IDT sublayer 213. In someembodiments, the first IDT sublayer 211 may include Aluminum (Al) andthe second IDT sublayer 213 may include tungsten (W). Other suitablematerials can be used for the first IDT sublayer 211 and/or second IDTsublayer 213, such as Aluminum (Al) copper (Cu), Magnesium (Mg),tungsten (W), titanium (Ti), or other suitable materials, as well as anysuitable combination thereof. In some embodiments, the IDT electrode 210may include alloys, such as AlMgCu, AlCu, etc. For example, the secondIDT sublayer 213 may include molybdenum (Mo).

A temperature compensation layer 230 is located over the IDT electrode210. In some embodiments, the temperature compensation layer 230 mayinclude a layer of silicon dioxide (SiO2) or other silica oxide-basedmaterial, although other suitable materials may also be used. In the SAWresonator 200 the temperature compensation layer 230 can bring atemperature coefficient of frequency (TCF) of the SAW resonator 200closer to zero. The temperature compensation layer 230 can have apositive TCF. This can compensative for a negative TCF of thepiezoelectric layer 202, as various piezoelectric layers such as lithiumniobate and lithium tantalate have a negative TCF. A passivation layer250 is located over the temperature compensation layer 230. Thepassivation layer 250 may include, for example, a layer of siliconnitride (SiN) or a layer of silicon oxynitride (SiON), although othersuitable materials may also be used.

In the illustrated embodiment, strips 242 (e.g., mass loading strips,metal strips, such as high density metal strips of any suitable metalwith a density equal to or greater than a layer of the IDT electrode210) are located over edge regions of the IDT 210 electrode. As can beseen in FIG. 5B, the IDT electrode 210 can include a bus bar 212 andfingers 214 that extend from the bus bar 212 toward the opposite busbar, with a gap portion or region 218 located between the ends of thefingers 214 and the opposite bus bar. The gap portions 218 can have awidth W₂. In some embodiments the gap portions 218 may have a width ofabout 0.9λ, although other suitable widths may also be used. The fingers214 of the IDT electrode 210 have an active region. The active regioncan be a region between the gap portions 218. This region can bereferred to as an aperture 226, having a width W₃. The edge portions 224on either side of a central region 228 of the active region or aperture126 have widths W₁. In some embodiments the edge portions 224 may have awidth of about 0.5 to 1.5 k, although other suitable widths may also beused. The strips 142 can overlie edge portions of fingers 214 of the IDTelectrode 210 as illustrated, and can have the same width W₁ as the edgeportions 224.

In the illustrated embodiment, the first IDT sublayer 211 has athickness T₂, the second IDT sublayer 213 has a thickness T₃, and thetemperature compensation layer 230 has a thickness of T₁ within the gapregions 218. The first IDT sublayer 211 includes extensions from the busbar 212 or dummy electrodes that extend into the gap region 218 and arespaced from end portions of the fingers 214. In some embodiments, thethickness T₂ may be between about 0.02λ and 0.1λ, although otherthicknesses may also be used. In some embodiments, the thickness T₃ maybe between about 0.02λ and 0.1λ, although other thicknesses may also beused. In some embodiments, the thickness T₁ of the temperaturecompensation layer 230 may be between about 0.2λ and 0.5λ, althoughother thicknesses may also be used.

With continued reference to FIG. 5A, the IDT 210 has reduced massloading in the gap portion or region 218. As illustrated in FIG. 5A, inone implementation the second IDT sublayer 213 is removed (e.g.,partially removed, completely removed) in the gap region 218, where thematerial of the second IDT sublayer 213 is more dense than the materialof the first IDT sublayer 211. Therefore, in one implementation, thereis only one IDT layer in the gap region 218 (e.g., the first IDTsublayer 213). In another implementation, some but less than all (e.g.,½, ¼) of the material of the second IDT sublayer 213 is removed in thegap region 218 so that the second IDT sublayer 213 is thinner in the gapregion 218 relative to other portions of the second IDT sublayer 213. Inone implementation, a stop layer (e.g., of titanium (Ti) or titaniumnitride (TiN)) can be included between the first IDT sublayer 211 andsecond IDT sublayer 213 to inhibit (e.g., prevent) removal (e.g.,etching) of the first IDT sublayer 211 int eh gap region 218 when thesecond IDT sublayer 213 is removed (e.g., etched) in the gap region 218.Such a stop layer would have no significant impact on performance of theSAW resonator 200 and aid in the manufacture thereof. The thickness ofthe IDT 210 in the gap region 218 is smaller relative to other portionsof the IDT 210. As further described below, the IDT 210 can be formed byfirst applying the first IDT sublayer 211, then applying the second IDTsublayer 213, then removing (e.g., etching) some or all of the materialof the second IDT sublayer 213 in the gap region 218. Advantageously,removing at least some (e.g., ½, ¾, removing all) of the second IDTsublayer 213 in the gap region 218 so that the first IDT sublayer 211provides the majority (e.g., all) of the IDT material in the gap region218 reduces mass loading in the gap region 218 to inhibit (e.g., reduce)Q degradation from resonant frequency (e.g., as a result of edge shearhorizontal mode radiation).

FIG. 5C illustrates a cross-section of a surface acoustic wave resonatorincluding a multi-layer piezoelectric substrate. The SAW resonator 200′of FIG. 5C is similar to the SAW resonator 200 in FIGS. 5A-5B. Thus,reference numerals used to designate the various components of the SAWresonator 200′ are identical to those used for identifying thecorresponding components of the SAW resonator 200 in FIGS. 5A-5B, unlessotherwise noted, except that a “′” is added to the numerical identifier.Therefore, the structure and description above for the various featuresof the SAW resonator 200 in FIGS. 5A-5B are understood to also apply tothe corresponding features of the SAW resonator 200′ in FIG. 5C, exceptas described below.

The SAW resonator 200′ includes a multilayer piezoelectric substrate206, including a support substrate 204 in addition to the piezoelectricsubstrate 202. The support substrate 204 may include silicon (Si) insome embodiments, although other suitable materials may also be used,including but not limited to sapphire, aluminum oxide (Al₂O₃), aluminumnitride (AlN), or ceramic materials. Although the multilayerpiezoelectric substrate 206 is illustrated as including two layers, oneor more additional layers may also be included. For example, in someembodiments, the multilayer piezoelectric substrate may include afunctional layer, such as an SiO₂ layer, between the piezoelectricsubstrate 202 and the support substrate 204. A multi-layer piezoelectricsubstrate can be implemented in accordance with any suitable principlesand advantages disclosed herein. Additionally, the second IDT sublayer213 is completely removed (e.g., etched) in the gap region 218. Inanother implementation, the second IDT sublayer 213 is completelyremoved (e.g. etched) in the gap region 218 and at least a portion ofthe first IDT sublayer 211 is removed (e.g., etched) in the gap region218.

FIG. 5D illustrates a cross-section of a surface acoustic wave resonatorincluding a multi-layer piezoelectric substrate. FIG. 5E is a top planview of the surface acoustic wave resonator of FIG. 5D. The SAWresonator 200A of FIGS. 5D-5E is similar to the SAW resonator 200 inFIGS. 5A-5B. Thus, reference numerals used to designate the variouscomponents of the SAW resonator 200A are identical to those used foridentifying the corresponding components of the SAW resonator 200 inFIGS. 5A-5B, except that an “A” is added to the numerical identifier.Therefore, the structure and description above for the various featuresof the SAW resonator 200 in FIGS. 5A-5B are understood to also apply tothe corresponding features of the SAW resonator 200A in FIGS. 5D-5E,except as described below.

The SAW resonator 200A includes a multilayer piezoelectric substrate206A, including a support substrate 204A disposed under thepiezoelectric substrate 202A, with an additional layer 205A (e.g.,functional layer) interposed between the support substrate 204A and thepiezoelectric substrate 202A. The support substrate 204A may includesilicon (Si) in some embodiments, although other suitable materials mayalso be used, including but not limited to sapphire, aluminum oxide(Al₂O₃), aluminum nitride (AlN), or ceramic materials. In oneimplementation, the piezoelectric substrate 202A may include lithiumniobate (LN). The additional layer 205A can be a low impedance layerthat has a lower acoustic impedance than the support substrate 204A. Insome implementations, the additional layer 205A can include a silicondioxide (SiO₂) layer. The additional layer 205A can increase adhesionbetween layers 202A, 204A of the multi-layer piezoelectric substrate206A. Alternatively or additionally, the additional layer 205A canincrease heat dissipation in the SAW device 200A relative to the SAWdevice 200, 200′. Although the multilayer piezoelectric substrate 206Ais illustrated as including three layers, more or fewer layers may beincluded. A multi-layer piezoelectric substrate can be implemented inaccordance with any suitable principles and advantages disclosed herein.Additionally, the second IDT sublayer 213 is completely removed (e.g.,etched) in the gap region 218.

FIG. 5F illustrates a cross-section of a surface acoustic wave resonatorincluding a multi-layer piezoelectric substrate. The SAW resonator 200Bof FIG. 5F is similar to the SAW resonator 200A in FIGS. 5D-5E. Thus,reference numerals used to designate the various components of the SAWresonator 200B are identical to those used for identifying thecorresponding components of the SAW resonator 200A in FIGS. 5D-5E,unless otherwise noted, except that a “B” is added to the numericalidentifier. Therefore, the structure and description above for thevarious features of the SAW resonator 200A in FIGS. 5D-5E are understoodto also apply to the corresponding features of the SAW resonator 200B inFIG. 5F, except as described below.

The SAW resonator 200B differs from the SAW resonator 200A in that thetemperature compensation layer (e.g., temperature compensation layer230A), passivation layer (e.g., passivation layer 250A) and strips(e.g., mass loading strips 242A) are excluded. The multilayerpiezoelectric substrate 206B includes a support substrate 204B disposedunder the piezoelectric substrate 202B, with an additional layer 205B(e.g., functional layer) interposed between the support substrate 204Band the piezoelectric substrate 202B. The support substrate 204B mayinclude silicon (Si) in some embodiments, although other suitablematerials may also be used, including but not limited to sapphire,aluminum oxide (Al₂O₃), aluminum nitride (AlN), or ceramic materials. Inone implementation, the piezoelectric substrate 202B may include lithiumtantalate (LT). The additional layer 205B can be a low impedance layerthat has a lower acoustic impedance than the support substrate 204B. Insome implementations, the additional layer 205B can include a silicondioxide (SiO₂) layer. The additional layer 205B can increase adhesionbetween layers 202B, 204B of the multi-layer piezoelectric substrate206B. Alternatively or additionally, the additional layer 205B canincrease heat dissipation in the SAW device 200B relative to the SAWdevice 200, 200′. Although the multilayer piezoelectric substrate 206Bis illustrated as including three layers, more or fewer layers may beincluded. A multi-layer piezoelectric substrate can be implemented inaccordance with any suitable principles and advantages disclosed herein.

FIG. 5G illustrates a cross-section of a surface acoustic wave resonatorincluding a multi-layer piezoelectric substrate. FIG. 5H is a top planview of the surface acoustic wave resonator of FIG. 5G. The SAWresonator 200C of FIGS. 5G-5H is similar to the SAW resonator 200A inFIGS. 5D-5E. Thus, reference numerals used to designate the variouscomponents of the SAW resonator 200B are identical to those used foridentifying the corresponding components of the SAW resonator 200A inFIGS. 5D-5E, unless otherwise noted, except that a “C” is added to thenumerical identifier. Therefore, the structure and description above forthe various features of the SAW resonator 200A in FIGS. 5D-5E areunderstood to also apply to the corresponding features of the SAWresonator 200C in FIGS. 5G-5H, except as described below.

The SAW resonator 200C differs from the SAW resonator 200A in that thetemperature compensation layer (e.g., temperature compensation layer230A), passivation layer (e.g., passivation layer 230A) and strips(e.g., mass loading strips 242A) are excluded. The multilayerpiezoelectric substrate 206C includes a support substrate 204C disposedunder the piezoelectric substrate 202C, with an additional layer 205C(e.g., functional layer) interposed between the support substrate 204Cand the piezoelectric substrate 202C. The support substrate 204C mayinclude silicon (Si) in some embodiments, although other suitablematerials may also be used, including but not limited to sapphire,aluminum oxide (Al₂O₃), aluminum nitride (AlN), or ceramic materials. Inone implementation, the piezoelectric substrate 202C may include lithiumtantalate (LT). The additional layer 205C can be a low impedance layerthat has a lower acoustic impedance than the support substrate 204C. Insome implementations, the additional layer 205C can include a silicondioxide (SiO₂) layer. The additional layer 205C can increase adhesionbetween layers 202C, 204C of the multi-layer piezoelectric substrate206C. Alternatively or additionally, the additional layer 205C canincrease heat dissipation in the SAW device 200C relative to the SAWdevice 200, 200′. Although the multilayer piezoelectric substrate 206Cis illustrated as including three layers, more or fewer layers may beincluded. A multi-layer piezoelectric substrate can be implemented inaccordance with any suitable principles and advantages disclosed herein.

The SAW resonator 200C also differs from the SAW resonator 200A in thatend portions of the fingers 214C have a bus bar connection portion 241Cthat extends from bus bar 212C, a widened portion 242C, a body portion243C, and an end or edge portion 224C. Both the end or edge portion 224Cand the widened portion 242C are wider than the other portions of thefinger 214C. The widened portion 242C and the end or edge portion 224Cof the finger 214C are included in border regions on opposing sides ofthe active region of the SAW resonator 200C that include the IDT 210C.The end or edge portions 224C and widened portions 242C of the fingers214C of the IDT 210C can have a square (e.g., hammerhead) shape and canmake the SAW resonator 200C a piston mode Lamb wave resonator.

FIGS. 6A-6C show steps in a process for making the IDT of a resonator R′using the SAW device 200 of FIGS. 5A-5B. As shown in FIG. 6A, the firstIDT sublayer 211 is applied (e.g., deposited), for example, over thepiezoelectric layer 202 and patterned. In one example, the first IDTsublayer 211 can be made of Aluminum (Al). As shown in FIG. 6B, thesecond IDT sublayer 213 is applied (e.g., deposited), for example, onthe first IDT sublayer 211 and the first and second IDT sublayers 211,213 are patterned to define the IDT structure of the SAW device 200 andthe acoustic reflectors 300. In one example, the second IDT sublayer 113can be made of tungsten (W). As shown in FIG. 6C, the piston mode layeror strips (e.g., mass loading strips) 242 can then be applied over theedge regions of the IDT 210 and patterned.

FIG. 7 is a top plan view of a surface acoustic wave filter including amulti-mode surface acoustic wave filter. The filter 400 includes threeSAW resonators 410 a, 410 b, and 410 c, as well as a multi-mode surfaceacoustic wave filter 460, referred to herein as an MMS 460. Althoughschematically illustrated as being shorter in length than the MMS 460,the SAW resonators 410 a, 410 b, and 410 c may in some embodiments besubstantially longer in length than the MMS 460, such that a reductionin length of the SAW resonators 410 a, 410 b, and 410 c can have asignificant impact on the overall wafer area occupied by the componentsof filter 400. A SAW device can in one implementation be a SAWresonator.

The MMS filter 460 is a type of an acoustic wave filter. The MMS filter460 includes a plurality of IDT electrodes that are longitudinallycoupled to each other and positioned between acoustic reflectors. SomeMMS filters are referred to as double mode surface acoustic wave (DMS)filters. There may be more than two modes of such DMS filters and/or forother MMS filters. MMS filters can have a relatively wide passband dueto a combination of various resonant modes. MMS filters can have abalanced (differential) input and/or a balanced output with properarrangement of IDTs. MMS filters can achieve a relatively low loss and arelatively good out of band rejection. In certain applications, MMSfilters can be receive filters arranged to filter radio frequencysignals. The MMS filter 460 can be included in a receive filter thatalso includes a plurality of acoustic resonators arranged in a laddertopology, for example, as shown in FIG. 7. The MMS filter 460 can betemperature compensated by including a temperature compensation layer,such as a silicon dioxide layer, over IDT electrodes. Such a temperaturecompensation layer can cause a temperature coefficient of frequency(TCF) of the MMS filter 460 to be closer to zero. In some instances, theMMS filter 460 can include a multi-layer piezoelectric substrate.

Each of the components of the filter 400 can include a high-densityinterdigital transducer electrode. Due to the reduced footprint of thefilter components, particularly the SAW resonators 410 a, 410 b, and 410c, the overall size of the wafer occupied by the filter components maybe reduced. However, the use of a denser IDT electrode in the MMS 460can alter the frequency response of the MMS 460.

In one implementation, the SAW resonators 410 a, 410 b and 410 c can besimilar to the SAW resonator 200 where the IDT 210 includes a first IDTsublayer 211 and a second IDT sublayer 213, the second IDT sublayer 213including a material of higher density (e.g., tungsten) than thematerial of the first IDT sublayer 211 (e.g., Aluminum). Similarly, theIDT electrodes of SAW devices in the MMS 460 can be similar to the SAWdevice 200. The SAW resonators 410 a, 410 b and 410 c can have a secondIDT sublayer 213 (e.g., including tungsten) with a greater thicknessthan the second IDT sublayer 213 of the IDT in the SAW devices of theMMS 460. For example, where the second IDT sublayer 213 of the SAWresonators 410 a, 410 b, 410 c includes tungsten (W), the second IDTsublayer 213 can have a thickness between about 0.04λ and 0.10λ.Alternatively, where the second IDT sublayer 213 of the SAW resonators410 a, 410 b, 410 c includes molybdenum (Mo), the second IDT sublayer213 can have a thickness of between about 0.06λ and 0.12λ. In oneimplementation, where the second IDT sublayer 213 of the IDT in the SAWdevices of the MMS 460 includes tungsten (W), the second IDT sublayer213 can have a thickness of between about 0.01λ and 0.04λ.Alternatively, where the second IDT sublayer 213 of the IDT in the SAWdevices of the MMS 460 includes molybdenum (Mo), the second IDT sublayercan have a thickness of between 0.02λ and 0.06 λ.

The different thicknesses of the second IDT sublayer 213 (e.g., layerincluding tungsten) can be achieved by etching some of the material ofthe second IDT sublayer 213 in the IDTs of the MMS 460 to achieve asmaller thickness of the second IDT sublayer 213 (e.g., of tungsten) forthe IDTs of the MMS 460 relative to the IDTs of the SAW resonators 410a, 410 b, 410 c. The different thicknesses of the second IDT sublayer213 of the IDTs in the SAW resonators 410 a, 410 b, 410 c relative tothose in the MMS 460 allow for partial slowdown of the IDT, and therebychange the acoustic performance of the IDTs on the same chip to optimizefor both the filter 400 performance and MMS 460 performance. Theimplementation shown on FIG. 7 advantageously allows for the MMS 460with the relatively thinner second IDT sublayer 213 to optimize itsperformance, along with the SAW resonators 410 a, 410 b, 410 c of thefilter 400 with relatively thicker second IDT sublayer 213 for sizereduction and to partially slow down the IDT, to be included on the samechip.

FIG. 8A is a top plan view of a structure 600 with two surface acousticwave resonators 610 a, 610 b disposed on a single wafer 602. FIG. 8Billustrates a cross-section of the structure 600 of FIG. 8A along thedashed line shown in FIG. 8A.

The structure 600 includes the single wafer 602 supporting the first SAWresonator 610 a and the second SAW resonator 610 b. The first SAWresonator 610 a has a multilayer IDT electrode with a first IDT sublayer611 a and a second IDT sublayer 613 a 230 a, while the second SAWresonator 610 b includes has a multilayer IDT electrode with a first IDTsublayer 611 b and a second IDT sublayer 613 b. The thickness of thesecond IDT sublayer 613 a of the IDT of the first SAW resonator 610 a isgreater (e.g., thicker) than the thickness of the second IDT sublayer613 b of the IDT of the second SAW resonator 610 b. The second IDTsublayers 613 a, 613 b can include a material with a higher density(e.g., tungsten) than the material (e.g., Aluminum) of the first IDTsublayers 611 a, 611 b. Optionally, the first IDT sublayer 611 a canhave the same thickness along the length of the fingers of the IDT.Optionally, the first IDT sublayer 611 b can have the same thickness asthe first IDT sublayer 611 a. In one implementation, the second IDTsublayer 613 a can have the same thickness along the length of thefingers of the IDT. In one implementation, the second IDT sublayer 613 bcan have the same thickness along the length of the fingers of the IDT.

The first SAW resonator 610 a and second SAW resonator 610 b are coveredby a temperature compensation layer 630 (e.g., including a silicondioxide, SiO2, material) and a passivation layer 650. The wafer 602material can in one implementation include lithium niobate (LN); othersuitable materials can be used. Strips (e.g., mass loading strips, metalstrips, such as high density metal strips of any suitable metal with adensity equal to or greater than a layer of the IDT electrode) 642 a,642 b are disposed over the end portions of the fingers of the IDT forthe first SAW resonator 610 a and second SAW resonator 610 b,respectively. The different thicknesses of the second IDT sublayer 613a, 613 b of the first and second SAW resonators 610 a, 610 b (e.g., theIDT sublayers with more dense material, such as tungsten) advantageouslyallow a variation in the mass loading of the resonators 610 a, 610 b onthe same wafer 602 (e.g., same chip), and allow adjustment of acousticproperties of the SAW resonators 610 a, 610 b without significantlyimpacting their electrical properties.

FIG. 9A is a top plan view of a structure 700 with two surface acousticwave resonators 710 a, 710 b disposed on a single wafer 702. FIG. 9Billustrates a cross-section of the structure 700 of FIG. 9A along thedashed line shown in FIG. 9A. The structure 700 of FIGS. 9A-9B issimilar to the structure 600 in FIGS. 8A-8B. Thus, reference numeralsused to designate the various components of the structure 700 areidentical to those used for identifying the corresponding components ofthe structure 600 in FIGS. 8A-8B, unless otherwise noted, except thatthe numerical identifier begins with a “7”. Therefore, the structure anddescription above for the various features of the structure 600 in FIGS.8A-8B are understood to also apply to the corresponding features of thestructure 700 in FIGS. 9A-9B, except as described below.

The structure 700 differs from the structure 600 in that at least aportion of (e.g., ½, ¾, all of) the second IDT sublayer 713 a of the IDTin the first SAW resonator 710 a is removed from the gap region of theIDT. Otherwise, as with the structure 600, the thickness of the secondIDT sublayer 713 a of the IDT in the first SAW resonator 710 a isgreater (e.g., thicker) than the second IDT sublayer 713 b of the IDT inthe second SAW resonator 710 b. Therefore, in one implementation the IDTfor the SAW resonator 710 a in the gap region only includes the firstIDT sublayer 711 a. In another implementation, the thickness of thesecond IDT sublayer 713 a of the IDT in the first SAW resonator 710 a isthinner in the gap region than in other portions of the second IDTsublayer 713 a, so that the gap region includes the first IDT sublayer711 a and the thinner portion of the second IDT sublayer 713 a.Advantageously, removing at least a portion of (e.g., ½, ¾, all of) thesecond IDT sublayer 713 a from the gap region for the IDT in the firstSAW resonator 710 a results in improved Q performance for the SAWresonator 710 a.

FIG. 10A is a top plan view of a structure 800 with two surface acousticwave resonators 810 a, 810 b disposed on a single wafer 802. FIG. 10Billustrates a cross-section of the structure 800 of FIG. 10A along thedashed line shown in FIG. 10A. The structure 800 of FIGS. 10A-10B issimilar to the structure 700 in FIGS. 9A-9B. Thus, reference numeralsused to designate the various components of the structure 800 areidentical to those used for identifying the corresponding components ofthe structure 700 in FIGS. 9A-9B, unless otherwise noted, except thatthe numerical identifier begins with a “8”. Therefore, the structure anddescription above for the various features of the structure 700 in FIGS.9A-9B are understood to also apply to the corresponding features of thestructure 800 in FIGS. 10A-10B, except as described below.

The structure 800 differs from the structure 700 in that the IDT of thefirst SAW resonator 810 a and second SAW resonator 810 b include dummyelectrodes that extend from the bus bar and are spaced apart from end oredge portions of the fingers of the IDT. Otherwise, as with thestructure 700, the thickness of the second IDT sublayer 813 a of the IDTin the first SAW resonator 810 a is greater (e.g., thicker) than thesecond IDT sublayer 813 b of the IDT in the second SAW resonator 810 b.As with the structure 700, removing at least a portion of (e.g., ½, ¾,all of) the second IDT sublayer 813 a from the gap region for the IDT inthe first SAW resonator 810 a advantageously results in improved Qperformance for the SAW resonator 810 a.

Piston mode Lamb wave resonators can be implemented in a variety ofways. As an example, a metal layout of an interdigital transducer of aLamb wave resonator can contribute to a velocity in a border regionhaving a lower magnitude than a velocity in an active region. Forinstance, an end portion of an interdigital transducer electrode fingercan have wider metal than the rest of the finger. Alternatively oradditionally, a bus bar can have a lower metal coverage ratio adjacentto an end portion of an interdigital transducer finger. As anotherexample, a layer over an interdigital transducer electrode cancontribute to a velocity in a border region having a lower magnitudethan a velocity in an active region. Such a layer can be over the activeregion to increase the magnitude of the velocity in the active regionrelative to the border region. Alternatively or additionally, a layerover the border region can reduce the velocity of the border regionrelative to the active region. Example embodiments of piston mode Lambwave resonators will be discussed with reference to FIGS. 11A-11E. Inthe Lamb wave resonators of any of FIGS. 11A-11E, an IDT can be onaluminum nitride piezoelectric layer. Any suitable principles andadvantages of the embodiments described herein can be combined with eachother. Any suitable principles and advantages of these embodiments canbe implemented in a piston mode Lamb wave resonator.

FIG. 11A illustrates an IDT 110A of a piston mode Lamb wave resonatoraccording to an embodiment. The IDT 110A includes fingers having hammerhead shaped end portions. The IDT 110A includes bus bars 112A and 117Aand a plurality of fingers extending from the bus bars 112A and 117A. Asillustrated, each of the fingers of the IDT 110A are substantially thesame. Finger 114A will be discussed as an example. Finger 114A has abody portion 115A that extends from bus bar 112A and an end portion116A. The end portion 116A is adjacent to the bus bar 117A. The endportion 116A is wider that the rest of the finger 114A. The end portion116A is hammer head shaped in plan view. The end portions (e.g., endportion 116A) of the fingers 114A of the IDT 110A can make the Lamb waveresonator a piston mode Lamb wave resonator.

FIG. 11B illustrates an IDT 110B of a piston mode Lamb wave resonatoraccording to another embodiment. The IDT 110B has with thicker portionsfor both border regions of each finger. The IDT 110B is like the IDT110A of FIG. 11A except that the fingers of the IDT 110B are wideradjacent to both bus bars 112B and 117B. Finger 114B will be discussedas an example. Finger 114B has a bus bar connection portion 121B thatextends from bus bar 112B, a widened portion 119B, a body portion 115B,and an end portion 116B. Both the end portion 116B and the widenedportion 119B are wider than the other portions of the finger 114B. Thewidened portion 119B and the end portion 116B of the finger 114B areincluded in border regions on opposing sides of the active region of theLamb wave resonator that include the IDT 110B. The end portions (e.g.,end portion 116B) and widened portions (e.g., widened portion 119B) ofthe fingers 114B of the IDT 110B can make the Lamb wave resonator apiston mode Lamb wave resonator.

FIG. 11C illustrates an IDT 110C of a piston mode Lamb wave resonatoraccording to another embodiment. The IDT 110C includes fingers havinghammer head shaped end portions and bus bars having extension portionsadjacent to the end portions of the fingers. The IDT 110C is like theIDT 110A of FIG. 11A except that the bus bars of the IDT 110C haveextension portions adjacent to end portions of fingers. Finger 114C hasa body portion 115D that extends from the bus bar 112C, 117C to an endportion 116C. Bus bars 112C and 117C each include extension portions,such as extension portion 123C, adjacent to end portions 116C of fingers114C of the IDT 110C. The extension portions of the bus bars 112C and117C can increase the metal coverage ratio around the border regionsrelative to the active region of the Lamb wave resonator. The endportions (e.g., end portion 116C) of the finger 114C and extensionportions (e.g., extension portion 123C) of the bus bars of the IDT 110Ccan make the Lamb wave resonator a piston mode Lamb wave resonator.

FIG. 11D illustrates an IDT 110D of a piston mode Lamb wave resonatoraccording to another embodiment. The IDT 110D has thicker end portionson border regions of each finger and bus bars having extension portionsadjacent to end portions of the fingers. The IDT 110D includes featuresof the IDT 110C of FIG. 11C and the IDT 110B of FIG. 11B. Finger 114Dhas a bus bar connection portion 121D that extends from bus bar 112D, awidened portion 119D, a body portion 115D, and an end portion 116D. Busbars 112D and 117D each include extension portions, such as extensionportion 123D, adjacent to end portions 116D of fingers 114D of the IDT110D.

FIG. 11E illustrates an IDT 110E of a piston mode Lamb wave resonatoraccording to another embodiment. The IDT 110E includes fingers havingthicker end portions and thicker regions extending from a bas bar towardan active region of the Lamb wave resonator. The IDT 110E is similar tothe IDT 110C of FIG. 11C except the fingers of IDT 110E include awidened portion extending from bus bars. As shown in FIG. 11E, finger114E of the IDT 110E includes widened portion 125E extending from thebus bar 112E to body portion 115E. The finger 114E also includes endportion 116E. Bus bars 112E and 117E each include widened extensionportions, such as widened extension portion 123E, adjacent to endportions 116E of fingers 114E of the IDT 110E.

FIG. 11F illustrates an IDT 110F of a piston mode Lamb wave resonatoraccording to another embodiment. The IDT 110F is similar to the IDT 110Bin FIG. 11B. Thus, the reference numerals used to designate the variouscomponents or features of the IDT 110F are identical to those used foridentifying the corresponding components or features of the IDT 110B inFIG. 11B, except that “F” instead of “B” has been added to the numericalidentifier. Therefore, the structure and description of the variouscomponents or features of the IDT 110B in FIG. 11B are understood toalso apply to the corresponding components or features of the IDT 110Fin FIG. 11F, except as described below.

The IDT 110F differs from the IDT 110B in that it includes a secondbusbar 118F spaced from the busbar 112F, 117F and the widened (e.g.,hammerhead) portion 119F, 116F. The second busbar 118F can have asmaller width (e.g., be narrower) than the busbar 112F, 117F. The secondbusbar 118F provides a mechanical mass loading effect to suppress higherorder transverse modes. The busbar 112F, 117F primarily supplieselectrical current for the IDT 110F. The IDT 110F has a low density IDTregion 120F as shown in FIG. 11F and further described below withreference to FIG. 11G.

FIG. 11G is a cross-sectional view of a SAW device 100F including theIDT 110F. The SAW device 100F is similar to the SAW device 100′ in FIG.1C. Thus, the reference numerals used to designate the variouscomponents or features of the SAW device 110F are identical to thoseused for identifying the corresponding components or features of the SAWdevice 100′ in FIG. 1C, except that “F” has been added to the numericalidentifier. Therefore, the structure and description of the variouscomponents or features of the SAW device 100′ in FIG. 1C are understoodto also apply to the corresponding components or features of the SAWdevice 100F in FIG. 11G, except as described below.

The SAW device 100F differs from the SAW device 100′ in that the massloading strips 142 in the SAW device 100′ are excluded from the SAWdevice 100F. In another implementation, mass loading strips (similar tothe mass loading strips 142 in the SAW device 100′) can be added to theSAW device 100F. Additionally, the SAW device 100F includes the secondbusbar 118F. In the illustrated embodiment, the second busbar 118F is adefined by first IDT sublayer 111F and second IDT sublayer 113F disposedover the first IDT sublayer 111F. As with the SAW device 100′, the firstIDT sublayer 111F can be of a material with a higher density than thematerial of the second IDT sublayer 113F. In some embodiments, the firstIDT sublayer 111F may include tungsten (W) and the second IDT sublayer113F may include Aluminum (Al). The portion of the IDT where the firstIDT sublayer 111F is thinned or removed and filled by the material ofthe second IDT sublayer 113F provides a low density IDT region 120Fbetween the busbar 112F, 117F and the second busbar 118F.

In another implementation, the SAW device 110F can instead have thefirst IDT sublayer 111F be of a material with a lower density (e.g.,Aluminum) than the material of the second IDT sublayer 113F (e.g.,tungsten) and the IDT 110F can have at least a portion (e.g., all) ofthe second IDT sublayer 113F removed between the busbar 112F, 117F andthe second busbar 118F (e.g., similar to the profile of the IDT 210shown in FIG. 5A), to provide the low density IDT region 120F betweenthe busbar 112F, 117F and the second busbar 118F.

FIG. 11H illustrates an IDT 110G of a piston mode Lamb wave resonatoraccording to another embodiment. The IDT 110G is similar to the IDT 110Fin FIG. 11F. Thus, the reference numerals used to designate the variouscomponents or features of the IDT 110G are identical to those used foridentifying the corresponding components or features of the IDT 110F inFIG. 11F, except that “G” instead of “F” has been added to the numericalidentifier. Therefore, the structure and description of the variouscomponents or features of the IDT 110F in FIG. 11F are understood toalso apply to the corresponding components or features of the IDT 110Gin FIG. 11H, except as described below.

The IDT 110G differs from the IDT 110F in that the second busbar 118G isdisconnected between fingers 114G of the IDT 110G. The disconnectedsecond busbar 118G provide mechanical mass loading to suppress higherorder transverse mode. The busbar 112G, 117G primarily supplieselectrical current for the IDT 110G. The IDT 110G has a low density IDTregion 120G as shown in FIG. 11H.

FIG. 11I is a cross-sectional view of a SAW device 100G including theIDT 110G. The SAW device 100G is similar to the SAW device 100F in FIG.11G. Thus, the reference numerals used to designate the variouscomponents or features of the SAW device 110G are identical to thoseused for identifying the corresponding components or features of the SAWdevice 100F in FIG. 11F, except that “G” instead of an “F” has beenadded to the numerical identifier. Therefore, the structure anddescription of the various components or features of the SAW device 100Fin FIG. 11F are understood to also apply to the corresponding componentsor features of the SAW device 100G in FIG. 11I, except as describedbelow.

The cross-section of the SAW device 100G in FIG. 11I is identical to thecross-section of the SAW device 100F in FIG. 11G. As with thedescription above for the SAW device 100F, mass loading strips (e.g.,similar to mass loading strips 142 in the SAW device 100′) canoptionally be included in the SAW device 100G. Additionally, the secondbusbar 118G is a defined by first IDT sublayer 111G and second IDTsublayer 113G disposed over the first IDT sublayer 111G. The first IDTsublayer 111G can be of a material with a higher density than thematerial of the second IDT sublayer 113G. In some embodiments, the firstIDT sublayer 111G may include tungsten (W) and the second IDT sublayer113G may include Aluminum (Al). The portion of the IDT where the firstIDT sublayer 111G is thinned or removed and filled by the material ofthe second IDT sublayer 113G provides a low density IDT region 120Gbetween the busbar 112G, 117G and the second busbar 118G. In anotherimplementation, the SAW device 110G can instead have the first IDTsublayer 111G be of a material with a lower density (e.g., Aluminum)than the material of the second IDT sublayer 113G (e.g., tungsten) andthe IDT 110G can have at least a portion (e.g., all) of the second IDTsublayer 113G removed between the busbar 112G, 117G and the secondbusbar 118G to provide the low density IDT region 120G between thebusbar 112G, 117G and the second busbar 118G. The mass loading providedby the disconnected second busbar 118G can be tuned by changing thewidth of the gap between an end of the disconnected busbar 118G and thenext finger 114G.

FIG. 11J illustrates an IDT 110H of a piston mode Lamb wave resonatoraccording to another embodiment. The IDT 110H is similar to the IDT 110Gin FIG. 11H. Thus, the reference numerals used to designate the variouscomponents or features of the IDT 110H are identical to those used foridentifying the corresponding components or features of the IDT 110G inFIG. 11H, except that “H” instead of “G” has been added to the numericalidentifier. Therefore, the structure and description of the variouscomponents or features of the IDT 110G in FIG. 11H are understood toalso apply to the corresponding components or features of the IDT 110Hin FIG. 11J, except as described below.

The IDT 110H differs from the IDT 110G in that the disconnected secondbusbar 118G in the IDT 110G is replaced by a floating mass loading strip118H that is spaced from the busbar 112H, 117H and the ends of thefingers 114H. The floating mass loading strip 118H provides mechanicalmass loading to suppress higher order transverse mode. The IDT 110H hasa low density IDT region 120H between the busbar 112H, 117H and thefloating mass loading strip 118H.

FIG. 11K is a cross-sectional view of a SAW device 100H including theIDT 110H. The SAW device 100H is similar to the SAW device 100G in FIG.11I. Thus, the reference numerals used to designate the variouscomponents or features of the SAW device 110H are identical to thoseused for identifying the corresponding components or features of the SAWdevice 100G in FIG. 11I, except that “H” instead of “G” has been addedto the numerical identifier. Therefore, the structure and description ofthe various components or features of the SAW device 100G in FIG. 11Iare understood to also apply to the corresponding components or featuresof the SAW device 100H in FIG. 11K, except as described below.

The cross-section of the SAW device 100H in FIG. 11K is identical to thecross-section of the SAW device 100G in FIG. 11I. As with thedescription above for the SAW device 100G, mass loading strips (e.g.,similar to mass loading strips 142 in the SAW device 100′) canoptionally be included in the SAW device 100H. Additionally, thefloating mass loading strip 118H is a defined by first IDT sublayer 111Hand second IDT sublayer 113H disposed over the first IDT sublayer 111H.The first IDT sublayer 111H can be of a material with a higher densitythan the material of the second IDT sublayer 113H. In some embodiments,the first IDT sublayer 111H may include tungsten (W) and the second IDTsublayer 113H may include Aluminum (Al). The portion of the IDT 110Hwhere the first IDT sublayer 111H is thinned or removed and filled bythe material of the second IDT sublayer 113H provides a low density IDTregion 120H between the busbar 112H, 117H and the floating mass loadingstrip 118H. In another implementation, the SAW device 110H can insteadhave the first IDT sublayer 111H be of a material with a lower density(e.g., Aluminum) than the material of the second IDT sublayer 113H(e.g., tungsten) and the IDT 110H can have at least a portion (e.g.,all) of the second IDT sublayer 113H removed between the busbar 112H,117H and the floating mass loading strip 118H to provide the low densityIDT region 120H between the busbar 112H, 117H and the floating massloading strip 118H. The mass loading provided by the floating massloading strip 118H can be tuned by changing the width of the gap betweenan end of the floating mass loading strip 118H and the next finger 114H.

FIG. 12 is a schematic diagram of a radio frequency module 1975 thatincludes a surface acoustic wave component 1976 according to anembodiment. The illustrated radio frequency module 1975 includes the SAWcomponent 1976 and other circuitry 1977. The SAW component 1976 caninclude one or more SAW resonators with any suitable combination offeatures of the SAW resonators disclosed herein. The SAW component 1976can include a SAW die that includes SAW resonators. The SAW die can alsoinclude one or more MMS filters. Some or all of the SAW resonators onthe SAW die can include a velocity reduction cover or another velocityadjustment structure.

The SAW component 1976 shown in FIG. 12 includes a filter 1978 andterminals 1979A and 1979B. The filter 1978 includes SAW resonators. Oneor more of the SAW resonators can be SAW resonators including a velocityreduction cover in accordance with any suitable principles andadvantages disclosed herein. The terminals 1979A and 1979B can serve,for example, as an input contact and an output contact. The SAWcomponent 1976 and the other circuitry 1977 are on or supported by acommon packaging substrate 1980 in FIG. 12. The package substrate 1980can be a laminate substrate. The terminals 1979A and 1979B can beelectrically connected to contacts 1981A and 1981B, respectively, on orsupported by the packaging substrate 1980 by way of electricalconnectors 1982A and 1982B, respectively. The electrical connectors1982A and 1982B can be bumps or wire bonds, for example. The othercircuitry 1977 can include any suitable additional circuitry. Forexample, the other circuitry can include one or more one or more poweramplifiers, one or more radio frequency switches, one or more additionalfilters, one or more low noise amplifiers, the like, or any suitablecombination thereof. The radio frequency module 1975 can include one ormore packaging structures to, for example, provide protection and/orfacilitate easier handling of the radio frequency module 1975. Such apackaging structure can include an overmold structure formed over thepackaging substrate 1975. The overmold structure can encapsulate some orall of the components of the radio frequency module 1975.

FIG. 13 is a schematic diagram of a radio frequency module 2084 thatincludes a surface acoustic wave component according to an embodiment.As illustrated, the radio frequency module 2084 includes duplexers 2085Ato 2085N that include respective transmit filters 2086A1 to 2086N1 andrespective receive filters 2086A2 to 2086N2, a power amplifier 2087, aselect switch 2088, and an antenna switch 2089. The radio frequencymodule 2084 can include a package that encloses the illustratedelements. The illustrated elements can be disposed on a common packagingsubstrate 2080. The packaging substrate can be a laminate substrate, forexample.

The duplexers 2085A to 2085N can each include two acoustic wave filterscoupled to a common node. The two acoustic wave filters can be atransmit filter and a receive filter. As illustrated, the transmitfilter and the receive filter can each be band pass filters arranged tofilter a radio frequency signal. One or more of the transmit filters2086A1 to 2086N1 can include one or more SAW resonators in accordancewith any suitable principles and advantages disclosed herein. Similarly,one or more of the receive filters 2086A2 to 2086N2 can include one ormore SAW resonators in accordance with any suitable principles andadvantages disclosed herein. In certain embodiments, one or more of thereceive filters 2086A2 to 2086N2 can include one or more SAW resonatorswith a velocity reduction cover and an MMS filter free from the velocityreduction cover. Although FIG. 13 illustrates duplexers, any suitableprinciples and advantages disclosed herein can be implemented in othermultiplexers (e.g., quadplexers, hexaplexers, octoplexers, etc.) and/orin switch-plexers.

The power amplifier 2087 can amplify a radio frequency signal. Theillustrated switch 2088 is a multi-throw radio frequency switch. Theswitch 2088 can electrically couple an output of the power amplifier2087 to a selected transmit filter of the transmit filters 2086A1 to2086N1. In some instances, the switch 2088 can electrically connect theoutput of the power amplifier 2087 to more than one of the transmitfilters 2086A1 to 2086N1. The antenna switch 2089 can selectively couplea signal from one or more of the duplexers 2085A to 2085N to an antennaport ANT. The duplexers 2085A to 2085N can be associated with differentfrequency bands and/or different modes of operation (e.g., differentpower modes, different signaling modes, etc.).

FIG. 14 is a schematic block diagram of a module 2190 that includes apower amplifier 2192, a radio frequency switch 2193, and duplexers 2191Ato 1291N in accordance with one or more embodiments. The power amplifier2192 can amplify a radio frequency signal. The radio frequency switch2193 can be a multi-throw radio frequency switch. The radio frequencyswitch 2193 can electrically couple an output of the power amplifier2192 to a selected transmit filter of the duplexers 2191A to 2191N. Oneor more filters of the duplexers 2191A to 2191N can include any suitablenumber of surface acoustic wave resonators which include a velocityreduction cover, in accordance with any suitable principles andadvantages discussed herein. In certain embodiments, one or more filtersof the duplexers 2191A to 2191N can include one or more SAW resonatorswith a velocity reduction cover and an MMS filter free from the velocityreduction cover. Any suitable number of duplexers 2191A to 2191N can beimplemented.

FIG. 15 is a schematic block diagram of a module 2295 that includesduplexers 2291A to 2291N and an antenna switch 2294. One or more filtersof the duplexers 2291A to 2291N can include any suitable number ofsurface acoustic wave resonators which include a velocity reductioncover, in accordance with any suitable principles and advantagesdiscussed herein. Any suitable number of duplexers 2291A to 2291N can beimplemented. The antenna switch 2294 can have a number of throwscorresponding to the number of duplexers 2291A to 2291N. The antennaswitch 2294 can electrically couple a selected duplexer to an antennaport of the module 2295.

FIG. 16 is a schematic diagram of a wireless communication device 2300that includes filters 2303 in a radio frequency front end 2302 accordingto an embodiment. The filters 2303 can include one or more SAWresonators in accordance with any suitable principles and advantagesdiscussed herein. The wireless communication device 2300 can be anysuitable wireless communication device. For instance, a wirelesscommunication device 2300 can be a mobile phone, such as a smart phone.As illustrated, the wireless communication device 2300 includes anantenna 2301, an RF front end 2302, a transceiver 2304, a processor2305, a memory 2306, and a user interface 2307. The antenna 2301 cantransmit RF signals provided by the RF front end 2302. Such RF signalscan include carrier aggregation signals. Although not illustrated, thewireless communication device 2300 can include a microphone and aspeaker in certain applications.

The RF front end 2302 can include one or more power amplifiers, one ormore low noise amplifiers, one or more RF switches, one or more receivefilters, one or more transmit filters, one or more duplex filters, oneor more multiplexers, one or more frequency multiplexing circuits, thelike, or any suitable combination thereof. The RF front end 2302 cantransmit and receive RF signals associated with any suitablecommunication standards. The filters 2303 can include SAW resonators ofa SAW component that includes any suitable combination of featuresdiscussed with reference to any embodiments discussed above.

The transceiver 2304 can provide RF signals to the RF front end 2302 foramplification and/or other processing. The transceiver 2304 can alsoprocess an RF signal provided by a low noise amplifier of the RF frontend 2302. The transceiver 2304 is in communication with the processor2305. The processor 2305 can be a baseband processor. The processor 2305can provide any suitable base band processing functions for the wirelesscommunication device 2300. The memory 2306 can be accessed by theprocessor 2305. The memory 2306 can store any suitable data for thewireless communication device 2300. The user interface 2307 can be anysuitable user interface, such as a display with touch screencapabilities.

FIG. 17 is a schematic diagram of a wireless communication device 2410that includes filters 2403 in a radio frequency front end 2402 andsecond filters 2413 in a diversity receive module 2412. The wirelesscommunication device 2410 is like the wireless communication device 2300of FIG. 16, except that the wireless communication device 2410 alsoincludes diversity receive features. As illustrated in FIG. 17, thewireless communication device 2410 includes a diversity antenna 2411, adiversity module 2412 configured to process signals received by thediversity antenna 2411 and including filters 2413, and a transceiver2404 in communication with both the radio frequency front end 2402 andthe diversity receive module 2412. The filters 2413 can include one ormore SAW resonators that include any suitable combination of featuresdiscussed with reference to any embodiments discussed above.

Any of the embodiments described above can be implemented in associationwith mobile devices such as cellular handsets. The principles andadvantages of the embodiments can be used for any systems or apparatus,such as any uplink wireless communication device, that could benefitfrom any of the embodiments described herein. The teachings herein areapplicable to a variety of systems. Although this disclosure includessome example embodiments, the teachings described herein can be appliedto a variety of structures. Any of the principles and advantagesdiscussed herein can be implemented in association with RF circuitsconfigured to process signals in a frequency range from about 30 kHz to300 GHz, such as in a frequency range from about 450 MHz to 8.5 GHz.

An acoustic wave resonator including any suitable combination offeatures disclosed herein can be included in a filter arranged to filtera radio frequency signal in a fifth generation (5G) New Radio (NR)operating band within Frequency Range 1 (FR1). A filter arranged tofilter a radio frequency signal in a 5G NR operating band can includeone or more acoustic wave resonators disclosed herein. FR1 can be from410 MHz to 7.125 GHz, for example, as specified in a current 5G NRspecification. One or more acoustic wave resonators in accordance withany suitable principles and advantages disclosed herein can be includedin a filter arranged to filter a radio frequency signal in a fourthgeneration (4G) Long Term Evolution (LTE) operating band and/or in afilter with a passband that spans a 4G LTE operating band and a 5G NRoperating band.

Aspects of this disclosure can be implemented in various electronicdevices. Examples of the electronic devices can include, but are notlimited to, consumer electronic products, parts of the consumerelectronic products such as die and/or acoustic wave components and/oracoustic wave filter assemblies and/or packaged radio frequency modules,uplink wireless communication devices, wireless communicationinfrastructure, electronic test equipment, etc. Examples of theelectronic devices can include, but are not limited to, a mobile phonesuch as a smart phone, a wearable computing device such as a smart watchor an ear piece, a telephone, a television, a computer monitor, acomputer, a modem, a hand-held computer, a laptop computer, a tabletcomputer, a personal digital assistant (PDA), a microwave, arefrigerator, an automobile, a stereo system, a DVD player, a CD player,a digital music player such as an MP3 player, a radio, a camcorder, acamera, a digital camera, a portable memory chip, a washer, a dryer, awasher/dryer, a copier, a facsimile machine, a scanner, amulti-functional peripheral device, a wrist watch, a clock, etc.Further, the electronic devices can include unfinished products.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,”“include,” “including” and the like are to be construed in an inclusivesense, as opposed to an exclusive or exhaustive sense; that is to say,in the sense of “including, but not limited to.” The word “coupled”, asgenerally used herein, refers to two or more elements that may be eitherdirectly connected, or connected by way of one or more intermediateelements. Likewise, the word “connected”, as generally used herein,refers to two or more elements that may be either directly connected, orconnected by way of one or more intermediate elements. Additionally, thewords “herein,” “above,” “below,” and words of similar import, when usedin this application, shall refer to this application as a whole and notto any particular portions of this application. Where the contextpermits, words in the above Detailed Description using the singular orplural number may also include the plural or singular numberrespectively. The word “or” in reference to a list of two or more items,that word covers all of the following interpretations of the word: anyof the items in the list, all of the items in the list, and anycombination of the items in the list.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the disclosure. Indeed, the novel apparatus, methods, andsystems described herein may be embodied in a variety of other forms;furthermore, various omissions, substitutions and changes in the form ofthe methods and systems described herein may be made without departingfrom the spirit of the disclosure. For example, while blocks arepresented in a given arrangement, alternative embodiments may performsimilar functionalities with different components and/or circuittopologies, and some blocks may be deleted, moved, added, subdivided,combined, and/or modified. Each of these blocks may be implemented in avariety of different ways. Any suitable combination of the elements andacts of the various embodiments described above can be combined toprovide further embodiments. The accompanying claims and theirequivalents are intended to cover such forms or modifications as wouldfall within the scope and spirit of the disclosure.

Features, materials, characteristics, or groups described in conjunctionwith a particular aspect, embodiment, or example are to be understood tobe applicable to any other aspect, embodiment or example described inthis section or elsewhere in this specification unless incompatibletherewith. All of the features disclosed in this specification(including any accompanying claims, abstract and drawings), and/or allof the steps of any method or process so disclosed, may be combined inany combination, except combinations where at least some of suchfeatures and/or steps are mutually exclusive. The protection is notrestricted to the details of any foregoing embodiments. The protectionextends to any novel one, or any novel combination, of the featuresdisclosed in this specification (including any accompanying claims,abstract and drawings), or to any novel one, or any novel combination,of the steps of any method or process so disclosed.

Furthermore, certain features that are described in this disclosure inthe context of separate implementations can also be implemented incombination in a single implementation. Conversely, various featuresthat are described in the context of a single implementation can also beimplemented in multiple implementations separately or in any suitablesubcombination. Moreover, although features may be described above asacting in certain combinations, one or more features from a claimedcombination can, in some cases, be excised from the combination, and thecombination may be claimed as a subcombination or variation of asubcombination.

Moreover, while operations may be depicted in the drawings or describedin the specification in a particular order, such operations need not beperformed in the particular order shown or in sequential order, or thatall operations be performed, to achieve desirable results. Otheroperations that are not depicted or described can be incorporated in theexample methods and processes. For example, one or more additionaloperations can be performed before, after, simultaneously, or betweenany of the described operations. Further, the operations may berearranged or reordered in other implementations. Those skilled in theart will appreciate that in some embodiments, the actual steps taken inthe processes illustrated and/or disclosed may differ from those shownin the figures. Depending on the embodiment, certain of the stepsdescribed above may be removed, others may be added. Furthermore, thefeatures and attributes of the specific embodiments disclosed above maybe combined in different ways to form additional embodiments, all ofwhich fall within the scope of the present disclosure. Also, theseparation of various system components in the implementations describedabove should not be understood as requiring such separation in allimplementations, and it should be understood that the describedcomponents and systems can generally be integrated together in a singleproduct or packaged into multiple products.

For purposes of this disclosure, certain aspects, advantages, and novelfeatures are described herein. Not necessarily all such advantages maybe achieved in accordance with any particular embodiment. Thus, forexample, those skilled in the art will recognize that the disclosure maybe embodied or carried out in a manner that achieves one advantage or agroup of advantages as taught herein without necessarily achieving otheradvantages as may be taught or suggested herein.

Conditional language, such as “can,” “could,” “might,” or “may,” unlessspecifically stated otherwise, or otherwise understood within thecontext as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements, and/or steps. Thus, such conditional language is notgenerally intended to imply that features, elements, and/or steps are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or without userinput or prompting, whether these features, elements, and/or steps areincluded or are to be performed in any particular embodiment.

Conjunctive language such as the phrase “at least one of X, Y, and Z,”unless specifically stated otherwise, is otherwise understood with thecontext as used in general to convey that an item, term, etc. may beeither X, Y, or Z. Thus, such conjunctive language is not generallyintended to imply that certain embodiments require the presence of atleast one of X, at least one of Y, and at least one of Z.

Language of degree used herein, such as the terms

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“about,” “generally,” and “substantially” as used herein represent avalue, amount, or characteristic close to the stated value, amount, orcharacteristic that still performs a desired function or achieves adesired result. For example, the terms “approximately”, “about”,“generally,” and “substantially” may refer to an amount that is withinless than 10% of, within less than 5% of, within less than 1% of, withinless than 0.1% of, and within less than 0.01% of the stated amount. Asanother example, in certain embodiments, the terms “generally parallel”and “substantially parallel” refer to a value, amount, or characteristicthat departs from exactly parallel by less than or equal to 15 degrees,10 degrees, 5 degrees, 3 degrees, 1 degree, or 0.1 degree.

The scope of the present disclosure is not intended to be limited by thespecific disclosures of preferred embodiments in this section orelsewhere in this specification, and may be defined by claims aspresented in this section or elsewhere in this specification or aspresented in the future. The language of the claims is to be interpretedbroadly based on the language employed in the claims and not limited tothe examples described in the present specification or during theprosecution of the application, which examples are to be construed asnon-exclusive.

Of course, the foregoing description is that of certain features,aspects and advantages of the present invention, to which variouschanges and modifications can be made without departing from the spiritand scope of the present invention. Moreover, the devices describedherein need not feature all of the objects, advantages, features andaspects discussed above. Thus, for example, those of skill in the artwill recognize that the invention can be embodied or carried out in amanner that achieves or optimizes one advantage or a group of advantagesas taught herein without necessarily achieving other objects oradvantages as may be taught or suggested herein. In addition, while anumber of variations of the invention have been shown and described indetail, other modifications and methods of use, which are within thescope of this invention, will be readily apparent to those of skill inthe art based upon this disclosure. It is contemplated that variouscombinations or subcombinations of these specific features and aspectsof embodiments may be made and still fall within the scope of theinvention. Accordingly, it should be understood that various featuresand aspects of the disclosed embodiments can be combined with orsubstituted for one another in order to form varying modes of thediscussed devices.

What is claimed is:
 1. An acoustic wave device comprising: apiezoelectric layer; and an interdigital transducer electrode includinga first layer disposed over the piezoelectric layer and a second layerdisposed over the first layer, the second layer being of a less densematerial than the first layer, a thickness of the first layer in a gapregion of the interdigital transducer electrode being smaller than athickness of the first layer in a center region of the interdigitaltransducer electrode to thereby reduce a mass loading of theinterdigital transducer electrode in the gap region.
 2. The acousticwave device of claim 1 wherein there is no first layer in the gapregion, the second layer being adjacent the piezoelectric layer in thegap region.
 3. The acoustic wave device of claim 1 wherein theinterdigital transducer electrode includes a first bus bar, firstfingers extending from the first bus bar, a second bus bar, and secondfingers extending from the second bus bar, the first and second bus barseach including the first and second layers.
 4. The acoustic wave deviceof claim 1 further comprising a temperature compensation layer disposedover the interdigital transducer electrode.
 5. The acoustic wave deviceof claim 4 further comprising a passivation layer disposed over thetemperature compensation layer.
 6. The acoustic wave device of claim 1further comprising a pair of mass loading strips disposed over theinterdigital transducer electrode, an edge of the mass loading stripsaligned with end regions of the interdigital transducer electrode. 7.The acoustic wave device of claim 1 wherein the piezoelectric layer is apart of a multilayer piezoelectric substrate, the multilayerpiezoelectric substrate additionally including a support substrateunderlying the piezoelectric layer.
 8. A radio frequency modulecomprising: a package substrate; an acoustic wave filter configured tofilter a radio frequency signal, the acoustic wave filter including anacoustic wave resonator that includes a piezoelectric layer and aninterdigital transducer electrode including a first layer disposed overthe piezoelectric layer and a second layer disposed over the firstlayer, the second layer being of a less dense material than the firstlayer, a thickness of the first layer in a gap region of theinterdigital transducer electrode being smaller than a thickness of thefirst layer in a center region of the interdigital transducer electrodeto thereby reduce a mass loading of the interdigital transducerelectrode in the gap region; and additional circuitry, the acoustic wavefilter and the additional circuitry disposed on the package substrate.9. The radio frequency module of claim 8 wherein there is no first layerin the gap region, the second layer being adjacent the piezoelectriclayer in the gap region.
 10. The radio frequency module of claim 8further comprising a temperature compensation layer disposed over theinterdigital transducer electrode.
 11. The radio frequency module ofclaim 10 further comprising a passivation layer disposed over thetemperature compensation layer.
 12. The radio frequency module of claim8 further comprising a pair of mass loading strips disposed over theinterdigital transducer electrode, an edge of the mass loading stripsaligned with end regions of the interdigital transducer electrode. 13.The radio frequency module of claim 8 wherein the piezoelectric layer isa part of a multilayer piezoelectric substrate, the multilayerpiezoelectric substrate additionally including a support substrateunderlying the piezoelectric layer.
 14. A wireless communication devicecomprising: an antenna; and a front end module including an acousticwave filter configured to filter a radio frequency signal associatedwith the antenna, the acoustic wave filter including one or moreacoustic wave devices that each include a piezoelectric layer and aninterdigital transducer electrode including a first layer disposed overthe piezoelectric layer and a second layer disposed over the firstlayer, the second layer being of a less dense material than the firstlayer, a thickness of the first layer in a gap region of theinterdigital transducer electrode being smaller than a thickness of thefirst layer in a center region of the interdigital transducer electrodeto thereby reduce a mass loading of the interdigital transducerelectrode in the gap region.
 15. The wireless communication device ofclaim 14 wherein there is no first layer in the gap region, the secondlayer being adjacent the piezoelectric layer in the gap region.
 16. Thewireless communication device of claim 14 further comprising atemperature compensation layer disposed over the interdigital transducerelectrode.
 17. The wireless communication device of claim 16 furthercomprising a passivation layer disposed over the temperaturecompensation layer.
 18. The wireless communication device of claim 14further comprising a pair of mass loading strips disposed over theinterdigital transducer electrode, an edge of the mass loading stripsaligned with end regions of the interdigital transducer electrode. 19.The wireless communication device of claim 14 wherein the piezoelectriclayer is a part of a multilayer piezoelectric substrate, the multilayerpiezoelectric substrate additionally including a support substrateunderlying the piezoelectric layer.